1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, an electronic device, a mobile object, and an oscillator manufacturing method.
2. Related Art
Various oscillators using a resonator (piezoelectric resonator) such as a crystal resonator or micro-electro-mechanical systems (MEMS) have been developed. Since there have been many requests for reducing the size of oscillators in recent years, oscillators having a minimum number of terminals exist. For example, there is a voltage-controlled temperature-compensated crystal oscillator (VC-TCXO) having only four terminals, i.e., a power terminal, a voltage control terminal (VC terminal), an output terminal, and a ground terminal. In such an oscillator having a small number of terminals, a dedicated terminal for inspection or adjustment cannot be provided.
JP-A-2009-201097 discloses a crystal oscillator which can be reduced in size by also using an inspection terminal of a crystal resonator as another terminal.
In the above-described voltage-controlled temperature-compensated crystal oscillator (VC-TCXO) with four terminals, when a terminal for adjusting temperature compensation characteristics is used also as a control terminal to adjust the temperature compensation characteristics, this control terminal is connected to, for example, an automatic frequency control (AFC) circuit during normal operation, and is connected to a temperature compensation circuit in adjusting the temperature compensation characteristics. Accordingly, during normal operation, a voltage according to an input voltage of the control terminal is applied, via the AFC circuit, to a variable capacity element for frequency control which is provided in an oscillation circuit. However, in adjusting the temperature compensation characteristics, the control terminal and the AFC circuit are disconnected from each other, and thus the voltage according to the input voltage of the control terminal is not applied. Therefore, in adjusting the temperature compensation characteristics, the temperature compensation characteristics are adjusted in a state in which the variable capacity element for frequency control has a capacity value different from that during normal operation. Accordingly, even when temperature compensation is correctly performed during normal operation, the load capacity of the oscillation circuit varies, and thus there is a concern that the oscillation circuit may have deteriorated frequency accuracy.